This invention relates to improvements in surge arresters of the type used for protecting telephone lines and other communication lines from overvoltage conditions.
One type of overvoltage or surge arrester used for protecting telephone lines comprises a housing that contains a pair of spaced carbon electrodes that define an arc or spark gap for grounding excessive line voltages so as to protect both equipment on the line and the line itself. In general the electrodes have opposed flat surfaces that define the arc gap. With repeated overvoltage conditions and discharges, carbon particles tend to erupt from the electrode surfaces. These particles sometimes become lodged between the electrodes causing a "noisy" line or even a complete grounding of the line.
In the design of surge arresters of the foregoing type a compromise is required between adequate surge life (i.e., number of firings) and acceptably low breakdown voltage. Thus, the arc gap can be widened to reduce the possibility of failure due to the presence of lodged carbon particles resulting from eruptions during firing. This will, of course, increase the surge life of the arrester. However, widening the arc gap may increase the breakdown voltage of the unit beyond acceptable standards.
The idea of providing a plurality of rectangular plateaus and grooves in the faces of the carbon electrodes for permitting erupted particles to be blown away from the arc gap is generally known from United States patents to DeKhotinsky 571,699 dated Nov. 17, 1896 and Yearance et al 3,703,665 dated Nov. 21, 1972. However, for a given size of electrodes it is believed that, in accordance with this invention, there should be only a single surface for arc discharge and a recess or valley area for receiving the erupted carbon particles, which recess area completely surrounds the single surface.